Coalescing agents are high boiling point solvents (that are slow to evaporate) used to reduce the minimum film formation temperature (MFFT) of paints, inks, other coating compositions and the like. In paint formulations in particular, coalescing agents act as temporary plasticizers to reduce the glass transition temperature (Tg) of the latex below that of the drying temperature to allow for good film formation.
Generally, coalescing agents function by softening the polymer particles in a latex, enabling the formation of a continuous film as the coating cures. To increase their effectiveness, is generally desirable for coalescing agents to have good hydrolytic stability and low water solubility.
Typical paint formulations can include one or more coalescing agents that range from 0.1 to 10% by weight that are used to promote the formation of a continuous film as the paint cures. This market has been historically dominated by volatile compounds such as 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate (commercially available from Eastman Chemical under the trade name TEXANOL®) or 2-ethylhexyl benzoate (commercially available from Velsicol Corporation under the trade name VELATE® 378). However, the emission of these volatile organic compounds (“VOC”) during the curing of paint has adverse environmental and health consequences.
Several approaches can be used to provide low- or zero-VOC latex paints. However, less desirable properties are often associated with these paints. For example, reactive diluents can be used to replace traditional coalescence solvents. But high reactive diluents have short shelf-lives and are not suitable for architectural paints, while low reactive diluents are not effective enough and have poor blocking resistance. Accordingly, there remains a need for low- or zero-VOC aqueous coating compositions that possess desirable properties, including good block resistance and scrub resistance.